Thank you, corn medical. From our coverage of the plane crash we move other big stories today. George zimmerman on trial or the death of trayvon martin. Today the father did everything to convince a jury that the cry on the audio tape was not zimmerman but his son. Reporter: Trayvon martin's father on the stand. My world has been turned upside down. Asked about this 9/11 call the night his son was shot. He's yelling help? Yes. I was listening to his life being taken. Reporter: Today he said the howls on the tape are his son's. I think the chairs had wheels on thaenld I find of pushed away from the table and just kind of shook my head and said I can't tell. Reporter: Homicide investigator says that's not what he told them when he first listened to it. He looked away and under his breath as I turntd it said no. Reporter: George zimmerman's fate could hinge on the screams and the defense played it for witness after witness, all zimmerman friends, all agreeing. That's george's voice. I thought it was george. Definitely it's georgie. They want to say he's the victim because now he's use self-defense. Reporter: Under cross-examination the detective noted when zimmerman heard the tape he didn't think it sounded like him either. I believe his words were that doesn't sound like me. Reporter: That audio is so crucial that 11 of the 12 defense witnesses have been asked about who was screaming. Tonight we learned another piece of evidence will be admissible. The amount of marijuana in trayvon martin's system. Now we head overseas to the

This transcript has been automatically generated and may not be 100% accurate.

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